Field of the Invention
The present invention relates to a supporting structure for a gear of an outboard motor. The present invention especially relates to a supporting structure for a driven gear provided to a shift mechanism of the outboard motor.
Description of the Related Art
A shift mechanism of an outboard motor intermits a rotative power and switches a rotation direction between a drive shaft and a propeller shaft that includes a pusher propeller. The drive shaft rotates by the rotative power output from a driving power source of the outboard motor. There has been provided this shift mechanism that includes, for example, a driving gear that rotates together with a drive shaft, a pair of driven gears that mesh with the driving gear and rotate in directions opposite from one another, and a clutch mechanism that intermits a rotative power between the pair of driven gears and a propeller shaft. With this shift mechanism, the clutch mechanism switches of which one of rotations of the pair of driven gears is transmitted to the propeller shaft. This can switch the rotation direction of a pusher propeller (that is, whether to move forward or move rearward).
There has been provided an outboard motor with regular rotation specification (hereinafter referred to as an “R/R specification”) and an outboard motor with a counter rotation specification (hereinafter referred to as a “C/R specification”). The outboard motor with R/R specification moves forward when a pusher propeller rotates to the right viewed from rearward and moves rearward when the pusher propeller rotates to the left. In contrast to this, the outboard motor with C/R specification moves forward when a pusher propeller rotates to the left viewed from rearward and moves rearward when the pusher propeller rotates to the right. Thus, a relationship between the travelling direction of the outboard motor and the rotation direction of the pusher propeller is the opposite between the outboard motor with R/R specification and the outboard motor with C/R specification. Accordingly, in the case where the R/R specification and the C/R specification share a shift mechanism, a relationship between a transmission of a rotative power to a propeller shaft through which one of a pair of driven gears and the front and rear movements of the outboard motor becomes the opposite between the R/R specification and the C/R specification. For example, generally, the pair of driven gears are arranged in a front-rear direction across a driving gear. With the R/R specification, the outboard motor moves forward when the rotative power is transmitted to the propeller shaft via the driven gear positioned on a front side. Accordingly, an application of the shared shift mechanism to the outboard motor with C/R specification moves the outboard motor forward when the rotative power is transmitted to the propeller shaft via the driven gear positioned on the rear side.
Generally, the outboard motor takes time for forward movement longer than the rearward movement and a load applied to the driven gear is also large. The increase in load applied to the driven gear displaces the driven gear and changes an abutment of teeth with the driving gear; therefore, service lives of the driving gear and the driven gear are likely to be short. Therefore, to share the shift mechanism between the R/R specification and the C/R specification, it is preferable that the driven gear positioned on the rear side (the driven gear that transmits the rotative power during the forward movement in the C/R specification) also has a configuration with which the displacement can be restrained in the case of the application of a large load. Japanese Laid-open Patent Publication No. 2012-187967 (hereinafter referred to as Patent Document 1) discloses a configuration applicable to both the specifications, R/R specification and C/R specification, to restrain a displacement of a gear. Japanese Laid-open Patent Publication No. 2013-107604 (hereinafter referred to as Patent Document 2) discloses a configuration for appropriate abutment of teeth between a driving gear and a driven gear even if a large load is applied to the driven gear. However, with the configuration described in Patent Document 1, since a thrust applied to a propeller shaft is transmitted to the driven gear. This varies a behavior of the driven gear according to the thrust applied to the propeller shaft, making the behavior unstable.
As a roller bearing (a bearing) to support the driven gear positioned on the rear side, a conical roller bearing (a conical bearing), which can bear a large load compared with a ball roller bearing (a ball bearing), is possibly applied. As a supporting structure for the conical roller bearing, for example, a differential gear mechanism for a four-wheeled vehicle possibly employs a configuration that includes an elastic body between two conical roller bearings arranged in directions opposite from one another. This configuration ensures stabilizing a preload applied to the two conical roller bearings and restraining a looseness of nuts securing the conical roller bearings. However, due to securement of an arrangement space and a restriction on attachment, the application of this configuration to the outboard motor is difficult.